Solid oxide fuel cells (“SOFC” below) use oxide ion conductive solid electrolytes; these are fuel cells which operate at comparatively high temperatures, to which electrodes are attached on both sides, and fuel gas is supplied to one side while oxidant (air, oxygen, etc.) is supplied to the other.
A fuel cell apparatus is described in Published Unexamined Patent Application 2010-277846 (Patent Document 1). In this solid oxide fuel cell apparatus, during the startup process a partial oxidation reforming reaction of the fuel, an autothermal reforming reaction in which the partial oxidation reforming reaction and steam reforming reaction are mixed, and a steam reforming reaction are successively caused to occur inside the reformer, and the temperatures of the reformer and the fuel cell stack are raised to the temperature at which the generating process is possible. Also, in this solid oxide fuel cell apparatus the fuel supply means, reforming air supply means, and water supply means are controlled so that a target fuel supply amount, target air supply amount, and target water supply amount are respectively supplied.
However in the fuel cell apparatus set forth in Published Unexamined Patent Application 2010-277846, water for steam reforming is intermittently supplied by a pulsed pump, so that after reforming water is supplied this water is vaporized in a short period, with the resulting problem that pressures inside the vaporization chamber and reformer temporarily rise. i.e., because it becomes difficult to supply fuel into the reformer when pressure inside the rated reference temperature is elevated, a fuel supply amount detection sensor detects the state whereby the fuel supply amount diminishes to less than the target amount under elevated pressure, judging immediately thereafter that fuel is insufficient, and performing an increase amount control to increase the supply of fuel. However, because in actuality the pressure drops in the next instant, it becomes easy to supply fuel, so that even though the above-described insufficient portion of fuel is not inherently required, it is still supplied, with the resulting problem that fuel is oversupplied.
This type of fuel oversupply problem occurs when there is an autothermal reforming reaction in the startup process, in which the amount of water supplied is particularly small. Therefore in the fuel cell apparatus set forth in Published Unexamined Patent Application 2010-277846, a stable autothermal reforming reaction can be implemented by suppressing changes in the amount of fuel supplied by the fuel supply means in the autothermal reforming reaction during the startup process.